If you plug in a laptop HD cable wrong by 1 pin then it can fry something expensive. A collegue did this and blew a bunch of fuses on a motherboard because 5V and ground ended up swapped over.

The power is right at the end of the connector and can be easily wired wrong if the connector isn't aligned.

I've plugged a desktop IDE drive in with the cable in backwards once though. It just refused to start up but once I swapped it over it worked fine. Teach me to not have proper cables with the key.

- Trevor